Of these eight, at least two give some information in their originals; the words "copyleft" and "no restriction, no copyright" seem to me pretty clear

Below line is original yoshi's postUnfortunately, there is no way to contact these authors, I'm afraid.

Haru, nabe, and SHI are the Japanese forum members, but none of them has logged in recently. For instance, Haru's last login was March...

And the other members are not even the forum members and there is no way to contact them... I can post a message on the Japanese wiki or somewhere, but even if there is a reply like "you can use my work as you want", there is no way to prove that this is really a reply from the author...

Does anyone know something about Michel Tsui (Evil)? We don't have any contact to him.

I can see on facebook quite a few people under this name, and with filtering through the additional info we could probably spam them all to make sure everything was tried... but that would be pretty desperate move!

Have you thought to check the old yahoo group? His contact information is in this post. There may be a lot of other people you can find through that group. This group may also be useful for finding older contributors.